Most system design and DSA content explains. chalk lets you run the idea.

Every topic is a sketch-style board with a short lesson, and 80+ labs let you move a dial and watch it break: shrink a cache, overload a queue, drop the reply on a payment. Some labs make you choose first, then show what your choice costs.

There are narrated videos and a review deck that brings questions back before you forget them. 500+ boards and 550+ lessons across system design, DSA, AI, databases, networking and more. The first three lessons of every track are free.